EDTA assisted phytorremediation of a Pb contamined soil: metal leaching and uptake by jack beans

Abstract

Lead (Pb) is one of the main soil contaminants. It is also of difficult phytoremediation due to its low solubility and high retention on soil particles. EDTA application to soil is a strategy to increase heavy metal phytoextraction, but such chelants usually cause phytotoxicity and metal leaching side effects. Therefore, these research work objectives were to evaluate the effects of single (0.5 g kg -1 ) and split (0.25 + 0.25 g kg -1 ) EDTA application on Pb uptake by jack beans (Canavalia ensiformis L.) as well as on Pb vertical movement in a Pb contaminated soil material. Two sets of experiments were carried out under greenhouse conditions: in the first one, plants were grown in 3L-pots filled with a Pb-contaminated soil to evaluate Pb uptake by plants; for the second experiment, PVC-columns (42 cm height) were used to evaluate soil Pb leaching: the upper half-column (20 cm) was filled up with Pb-contaminated soil (1800 mg kg -1 ) whereas the lower half-column (20 cm) was filled with clean soil. Ten 60 mm-rainfalls with a duration of five hours were simulated by dropping distilled water on the top of columns, and leachates were collected for chemical analysis. Plants did not show any visual Pb toxicity symptoms or reduction in dry matter yield. Nevertheless, Pb uptake by jack beans regarded as total plant Pb accumulation was higher in EDTA-treated plants. Vertical Pb movement was observed mostly for the single EDTA application. EDTA addition to the soil favor Pb-phytoextraction by jack beans and the split EDTA application decrease the metal leaching, indicating less risk of environmental contamination. Key words: Canavalia ensiformis L., lead, phytoremediation, chelant LIXIVIAÇÃO E ABSORÇÃO DE Pb PELO FEIJÃO-DE-PORCO ASSISTIDO PELA APLICAÇÃO DE EDTA NO SOLORESUMO: O chumbo (Pb) é um dos principais contaminantes de solo. Os processos de remediação são dificultados devido à alta retenção do elemento às partículas do solo. A utilização do EDTA para aumentar a fitoextração dos metais do solo tem apresentado bons resultados. Contudo, os quelantes podem causar efeitos indesejáveis como a fitotoxidez e a lixiviação do metal. Nesse sentido, avaliouse o efeito da aplicação única (0,5 g kg -1 ) e parcelada de EDTA (0,25 + 0,25 g kg -1 ) na absorção de Pb pelas plantas de feijão-de-porco (Canavalia ensiformis L.) e na movimentação vertical de Pb em solo contaminado, sob condições de casa de vegetação. Em um experimento, as plantas foram crescidas em vasos contendo 3 L de solo contaminado por Pb. No outro, utilizaram-se colunas de PVC com 42 cm de altura, preenchendo-se os primeiros 20 cm com solo contaminado com 1800 mg kg -1 de Pb, seguido de outros 20 cm, com amostra de solo não contaminado. Nesse experimento, foram feitas dez lixiviações com água em volume equivalente a uma chuva de 60 mm cada. As plantas não apresentaram sintomas visuais de toxicidade de Pb, nem diferença na produção de massa seca do feijão em função dos tratamentos aplicados. No entanto, a absorção de Pb foi superior para as plantas que r...

Phytoremediation of lead by jack beans on a Rhodic Hapludox amended with EDTA

“…This positive findings disagree with Geebelen et al (2002) and Wang et al (2007) who found reduction in shoot length and weight of bean (Phaseolus vulgaris L.) and Bibens maximowicziana L. after increasing Pb rates and EDTA addition. Results of this study indicate a good potential of the jack bean as a Pb phytoextractor plant due to its high dry matter yield on tropical soils, which was confirmed by Gabos et al (2009). On the other hand, for treatments without EDTA, shoot dry matter yields decreased with increasing Pb rates and presented the lowest yield at the highest Pb rate (2,400 mg kg -1 ).…”

“…However, although the biomass production of tropical species is generally high, only few studies have been carried out with the objective to identify tropical species with good phytoextraction potential. In addition few studies have been carried out with tropical soils and phytoextraction (Gabos et al, 2009).…”

“…In this context EDTA is considered the most effective one (Huang et al, 1997;Shen et al, 2002;Saifullah et al, 2009), although a main problem of its use is the leaching of Pb-EDTA with subsequent risk of groundwater contamination. On the other hand, because the major part of Pb-EDTA is taken up in short time (6 h) (Shen et al, 2002), various studies have reported significant leaching reduction by splitting the EDTA application (Grcman et al, 2001;Wenzel et al, 2003;Gabos et al, 2009). Brazilian soils are highly weathered with deep profiles (> 20 m) dominated by hydrous oxides of Fe and Al (Brady and Weil, 1999) that form inner-sphere complex with Pb 2+ (Sparks, 1995).…”

Lead sorption and leaching from an Inceptisol sample amended with sugarcane vinasse

“…This is related to the binding between organic compounds of vinasse and Pb in the soil solution, which enhanced mobility through the soil columns, under the successive leaching. Similar results were found for soil columns under the influence of EDTA in an Oxisol (Gabos et al, 2009), and citrate and oxalate in a Spodosol (Freitas et al, 2009) columns (the same size used in this work) was enhanced when soils were treated with two wastewaters from an agricultural industry (olive-mill wastewater and concentrated sugarbeet vinasse) (Madrid and Díaz-Barrientos, 1998).…”

Vegetable species for phytoextraction of boron, copper, lead, manganese and zinc from contaminated soil

“…Among the few studies available in Brazil, many have been restricted to academics (Carneiro et al, 2001;Coscione and Berton, 2009;Gabos et al, 2009;Marques et al, 2000;Pereira et al, 2007;Romeiro et al, 2006;Santos et al, 2007;Zeittouni et al, 2007). In spite of that, promising species well known in Brazilian agriculture due to its robustness, good climate adaptation, deep root system and good biomass production have not been evaluated.…”